The invention relates to a method and a device for purification of deicing fluid for recovery of glycol, especially purification of deicing fluids from airports, wherein initially solid particles are separated, then dissolved organic compounds and positive and negative ions are separated by ion exchange in an ion exchanger, and finally water is separated by distillation.
Accumulation of ice on aircraft wings is a well known problem involving great risks in that the surface of the foil changes and in that the weight of the aircraft increases. At present, ice is removed from the wings of the aircraft by spraying them with so called deicing fluid, usually consisting of ethylene glycol, propylene glycol or a mixture thereof and additives of different kinds.
For economical reasons and in order to minimize the environmental impact, it is desirable to recover the deicing fluid to the greatest extent possible. At present, processes exist to purify and concentrate the most common deicing fluid which normally consists of pure glycol (monopropylene, monoethylene or diethylene) having additives of anionic and/or non-ionic tensides, corrosion inhibitors and, in certain cases, colourings and water.
Further development of deicing fluids has, however, resulted in the development of new types having the above mentioned deicing fluid as a basis with the addition of a thickener, the purpose of which is to accomplish a better protection against renewed freezing of the deicing fluid due to fact that the thickener obtains a higher viscosity and therefore remains for a longer time period on an aircraft. This is of great importance on airports having very frequent traffic. The aircraft may then have to wait for long periods of time before takeoff, and it is then of utmost importance that the deicing fluid remains. When the aircraft takes off, the deicing fluid is sheared off.
For the time being, commercial recovery processes comprise filtration, deionization and distillation. The used deicing fluid is collected in the deicing plant and when it enters the recovery plant it normally has a glycol content of about 15-25% by weight in a mixture with water, solid particles, salts, etc. The initial filtration is, for instance, presently accomplished in a cotton filter having a mesh width of down to about 5-10 xcexcm. After filtration, the deicing fluid is passed through ion exchange filters to separate dissolved organic compounds and positive and negative ions. Subsequently, water in the deicing fluid is separated by distillation, possibly under vacuum, until the mixture of glycol/water has obtained the desired concentration.
However, at airports, where deicing fluid comprising thickener is used, problems arise in connection with the recovery of glycol. The thickener comprises a polymer, a polar organic compound, and long polymer chains thereof block the material in the ion exchange plant. The capacity of the ion exchange material is then strongly reduced with extensive operational breakdowns as a result. The capacity of the ion exchange material is also reduced by anionic tensides and petroleum products, e.g. hydraulic oil, aircraft fuel etc., which, in many cases, contaminate the glycol.
A process for recovery of glycol, among other things deicing fluid, is for instance disclosed in the Canadian Patent Application CA-A1-2116827. In this purification process fats, oils, and dirt are first separated from the used glycol in a sedimentation tank having a partition wall consisting of a metal mesh. The fluid is left to stand in the sedimentation tank until heavy solid particles have fallen down to the bottom of the tank and light organic compounds, such as fuel and hydraulic oils, float on the surface. The organic compounds are then removed from the surface by means of a pump. Purified glycol is removed from the sedimentation tank as an intermediate phase for further purification in a column packed with packing material of stainless steel, wherein water is evaporated by means of hot air before the glycol is further purified and concentrated by vacuum distillation. The vaporized water containing buffer, volatile organic compounds and other additives occurring in the deicing fluid must then be purified in a separate process.
The object of the invention is to remove the above referenced drawbacks with the method of the invention.
The object of the invention is also to achieve a device for purification of deicing fluid for recovery of glycol.
Due to the method and the device according to the invention, organic compounds, such as thickener, petroleum products and anionic tensides occurring in the deicing fluid, may be separated from the deicing fluid. In this way, damage on the material in the ion exchangers is avoided, and, according to the invention, allowing all kinds of deicing fluids to be purified and recovered with a higher degree of purification than has earlier been possible to achieve. A high degree of purification of the water separated during distillation is also achieved, said water not requiring any extra purification but can be discharged directly to the sewage system.